Timer APIs: setTimeout, setInterval, requestAnimationFrame #110

Implement timer APIs and the event loop infrastructure needed to schedule callbacks.

Scope#

Event Loop#

• Implement a basic event loop that processes:
  • Microtasks (Promise callbacks — already have microtask queue in Promise impl)
  • Macrotasks (timer callbacks)
  • Animation frame callbacks
• The event loop should integrate with the platform crate's run loop (AppKit NSRunLoop)
• Provide a way to pump the event loop from tests without a real window

Timer Functions (globals)#

• setTimeout(callback, delay) — schedule callback after delay (ms), return timer ID
• clearTimeout(id) — cancel a pending timeout
• setInterval(callback, delay) — schedule repeating callback, return timer ID
• clearInterval(id) — cancel a repeating timer
• Timer IDs are positive integers, monotonically increasing
• Delay of 0 or negative should still be deferred (not synchronous)
• Support string argument to setTimeout (eval — lower priority, can skip)

requestAnimationFrame#

• requestAnimationFrame(callback) — schedule callback before next repaint, return ID
• cancelAnimationFrame(id) — cancel a pending animation frame
• Callback receives a DOMHighResTimeStamp argument (milliseconds since page load)
• In test mode, can use a fake timestamp

Timer Storage#

• Maintain a timer heap or sorted list of pending timers
• Each timer: { id, callback (GcRef), delay, interval (bool), scheduled_at }
• Timer callbacks must be GC roots while pending
• Cleared timers should release their callback references

Integration with Microtasks#

• After each macrotask (timer callback), drain the microtask queue
• This ensures Promise .then() callbacks run between timer callbacks
• Order: run macrotask → drain microtasks → next macrotask

Acceptance Criteria#

• setTimeout(fn, 100) executes fn after ~100ms
• clearTimeout(id) prevents execution
• setInterval(fn, 100) executes fn repeatedly
• clearInterval(id) stops repetition
• setTimeout(fn, 0) defers execution (not synchronous)
• requestAnimationFrame(fn) schedules before next paint
• Timer callbacks run after microtask queue drains
• Timer IDs are unique positive integers
• Testable without a real window/run loop

Phase 11 — DOM-JS Bindings (issue 5 of 8). Depends on: issue 1 (Console API, for testing output).